Antimicrobial materials are well known in the art. A well known antimicrobial material is natamycin. Natamycin is a polyene macrolide natural antifungal agent produced by fermentation of the bacterium Streptomyces natalensis. Natamycin (previously known as pimaricin) has an extremely effective and selective mode of action against a very broad spectrum of common food spoilage yeasts and moulds with most strains being inhibited by concentrations of 1-15 ppm of natamycin.
Natamycin is accepted as a food preservative and used world wide, particularly for surface treatment of cheese and dried fermented sausages. It has several advantages as a food preservative, including broad activity spectrum, efficacy at low concentrations, lack of resistance, and activity over a wide pH range. Neutral aqueous suspensions of natamycin are quite stable, but natamycin has poor stability in acid or alkaline conditions, in the presence of light, oxidants and heavy metals. For example, natamycin can be used in pasteurised fruit juice to prevent spoilage by heat-resistant moulds such as Byssochlamys. The acid pH of the juice, however, promotes degradation of natamycin during pasteurisation as well as during storage if the juice is not refrigerated. Natamycin is also degraded by high temperature heat processing, such as occurs during cooking of bakery items in an oven.
At extreme pH conditions, such as pH less than 4 and greater than 10, natamycin is rapidly inactivated with formation of various kinds of decomposition products. Acid hydrolysis of natamycin liberates the inactive aminosugar mycosamine. Further degradation reactions result in formation of dimers with a triene rather than a tetraene group. Heating at low pH may also result in decarboxylation of the aglycone. Alkaline hydrolysis results in saponification of the lactone. Both acid degradation products (aponatamycin, the aglycone dimer, and mycosamine), and alkaline or UV degradation products proved even safer than natamycin in toxicology tests, but are inactive biologically.
Natamycin is generally dosed into or onto food as a powder or as an aqueous natamycin suspension. This kind of dosage form leaves the natamycin unprotected under the conditions of processing and use. The natamycin powder, although mixed with excipients such as lactose, may also be sticky to handle and cause dust problems within the food processing plants. Furthermore, natamycin is so highly effective as an antifungal compound that it may adversely affect the processing of the products that it is intended to preserve if this is dependent on desired fungal activity. There is thus a need for a protected dosage form of natamycin.
A general description of natamycin and its current uses may be found in Thomas, L. V. and Delves-Broughton, J. 2003. Natamycin. In: Encyclopedia of Food Sciences and Nutrition. Eds. B. Caballero, L. Trugo and P. Finglas, pp 4109-4115. Elsevier Science Ltd.
Bacteriocins are antimicrobial proteins or peptides that can be produced by certain bacteria, which can kill or inhibit the growth of closely related bacteria. The bacteriocins produced by lactic acid bacteria are of particular importance since they have great potential for the preservation of food and for the control of foodborne pathogens. (Wessels et al. 1998.)
The most well known bacteriocin is nisin, which is the only bacteriocin currently authorised as a food additive. Nisin is produced by fermentation of the dairy starter culture bacterium Lactococcus lactis subsp. lactis, and is sold as the commercial extract Nisaplin® Natural Antimicrobial (Danisco). Nisin has an unusually broad antimicrobial spectrum for a bacteriocin, being active against most Gram-positive bacteria (e.g. species of Bacillus, Clostridium, Listeria, lactic acid bacteria). It is not normally effective against Gram-negative bacteria, yeasts or moulds. Nisin is allowed as a food preservative worldwide but its levels of use and approved food applications are strictly regulated, varying from country to country.
Other bacteriocins have since been discovered with potential as food preservatives, e.g. pediocin, lacticin, sakacin, lactococcin, enterococin, plantaricin, leucocin. These are also active, although usually with a more narrow spectrum, against Gram-positive bacteria. Their food use is at present restricted to production of the bacteriocin in situ, i.e. by growth of the producer organism within the food.
Food safety and prevention of food spoilage is an ever present concern worldwide, particularly with the increasing trend for convenience foods such as ready to eat meals, soups, sauces or snacks. Spoilage of food is a major economic problem for the food manufacturer. Food manufacturers need to protect the health and safety of the public by delivering products that are safe to eat. Such food must have a guaranteed shelf life, either at chilled or ambient temperature storage. Consumers prefer good tasting food of high quality—this is difficult to achieve with chemical preservatives, harsh heating regimes and other processing measures. Food safety and protection is best achieved with a multiple preservation system using a combined approach of milder processing and natural preservatives. Foodborne micro-organisms are also less able to adapt and grow in food preserved with different preservative measures.
There is much concern about food safety and the growth of food pathogens such as Listeria monocytogenes. This particular pathogen can grow at low temperatures, which are often used as an additional preservative measure. Foodborne pathogens can sometimes adapt to different preservatives and storage conditions, thus a combination of preservative measures can be more successful than individual measures.
Cooked meat joints are new generation, convenience products now on offer to consumers. The preparation of these meat joints usually involves injection or tumbling of the raw meat in polyphosphate brine to increase the meat's tenderness, moistness and volume. The meat is then cooked before distribution to retail outlets and its subsequent consumer purchase and consumption.
The majority of processes for these meats now involve the ‘cook-in’ system in which the meat is cooked in plastic bags or film. Whole joints may be de-boned, pumped with polyphosphate brine and tumbled or massaged for a short period. This distributes the brine evenly and also achieves a layer of exudate on the surface that helps the plastic packaging to adhere closely to the meat surface. Large joints are usually gas or vacuum-packaged into plastic bags. These cooked meat products are often considered to be of good quality and healthy, since they may be low in fat with minimal salt content. They may not necessarily be re-heated by the purchaser prior to consumption.
These minimally processed products rely on refrigeration to ensure stability and safety of the cooked meat during shelf life, which may be as long as 90 days (Varnam and Sutherland, 1995). Spoilage of the cooked meats, if post-processing contamination is not a factor, would be due to the Gram-positive heat-resistant bacteria Bacillus and Clostridium, particularly if the meat is exposed to temperatures above 7° C. Spoilage due to these organisms can be rapid if the meat is exposed to temperatures as high as 15° C. or above. If the meat has not been sufficiently cooked, Enterococcus or heat-resistant Lactobacillus species may survive, many of which can grow at refrigeration temperatures. If the product has been handled after cooking then re-packaged and vacuum-packed, spoilage is often associated with Lactobacillus, Leuconostoc or Carnobacterium. Brochothrix thermosphacta, another Gram-positive bacterium, can also cause problems. Gram-negative bacteria will only be a problem in unpackaged cooked meats, or those that are packed in air-permeable film. Moulds may develop on cooked meat joints that have been exposed to air and whose surfaces have dried out. There is also concern over post-processing contamination and growth of Listeria monocytogenes, a foodborne pathogen that can grow at refrigeration temperatures. It would be a benefit to both the public in terms of safety and manufacturers in terms of economics and reputation, if an effective preservative could be somehow applied to the surface layer of the cooked meat.
Raw, whole muscle meat is also being increasingly sold as a chilled convenience meat product that is ready prepared and tenderised for the consumer to cook. The meat is usually covered with a marinade then vacuum-packed in a clear pouch. The marinade may be applied and simply left to soak into the meat surface, or the meat may be tumbled in the marinade to increase its tenderising effect and penetration. This vacuum-packed, marinated fresh meat can be kept for up to 28 days at refrigeration temperatures before purchase by the consumer and subsequent cooking at home. These meat products are considered value-added fresh meats and cover a wide range of raw meats (pork, chicken, beef, ground beef, steaks, diced meats, joints, etc.). The combination of the acidic nature of the marinade and the lack of oxygen in the vacuum-packed pouches means that Gram-positive lactic acid bacteria are associated with spoilage of these products (Susiluoto et al. 2003).
Nisin is a natural preservative that has been used safely in food for nearly 50 years. It is effective against Gram-positive bacteria including lactic acid bacteria, Brochothrix thermosphacta, Listeria monocytogenes, Bacillus and Clostridium. As the spoilage associated with both the meat products described above, is usually caused by Gram-positive bacteria, nisin could be considered as part of a preservative system to guarantee or extend shelf life. However the environment of both meat products is not favourable to nisin stability or activity. Brine and polyphosphate solutions used to inject raw meat are usually at alkaline pH. Nisin stability is optimum at pH 3 (Davies et al. 1998). The cooking process, particularly at high or neutral pH conditions, would lead to significant nisin degradation. In raw meat, nisin is vulnerable to degradation by proteases. A more specific concern is the inactivation of nisin in raw meat by the formation of an adduct with glutathione in an enzyme-mediated reaction (Rose et al. 1999, 2002, 2003).
Numerous prior art teachings have discussed potential uses of nisin in foodstuffs. Examples are:                Caserio et al. (1979) describes research on the use of nisin in cooked, cured meat products. Mortadella, wurstel sausage, prosciutto. The target organisms: Staphylococcus, sulphate-reducing clostridia. Prosciutto had nisin injected with brine after dissolution in dilute lactic acid.        Gola (1962) incorporated nisin into the gelatine for canning of large hams. In the first experiment, brines for injection were acidified to facilitate nisin solubility.        Taylor & Somers (1985) evaluate the antibotulinal effectiveness of nisin in bacon. Nisin was included in brine formulation injected into pork belly.        Usborne et al. (1986) discusses sensory evaluation of nisin-treated bacon. Nisin was added to brine pumping solution before injection into the bacon.        US 2003/0108648 relates to compositions having bacteriostatic and bactericidal activity against bacterial spores and vegetative cells and process for treating foods therewith.        U.S. Pat. No. 6,207,210 relates to broad-range antibacterial composition and process of applying to food surfaces        EP0770336 describes injection of meat trimmings/brine solution in which a starter culture has produced a bacteriocin.        Article found at http://www.nai.usda.gov/fsrio/ppd/ars010f.htm on work at Meat Research Unit, MARC mentions a presentation on ‘antibacterial properties of injectable beef marinades’.        WO2003/11058 relates to food preservation formulation comprising compound(s) derived from natural sources. Natural compounds are formulated and application to a food and irradiation at <3 kGy results in decrease of microflora compared to non-irradiated controls. Nisin is a preferred compound.        US 2003/0108648 teaches nisin as part of a combination for marinades        
The above extensive prior art does not address or solve the problems of protection of antimicrobial materials such as nisin from environments, such as those in meat products, which are not favourable to the stability or activity of the antimicrobial material
The present invention alleviates the problems of the prior art.
In one aspect the present invention provides an antimicrobial material in an encapsulated form, comprising a core of antimicrobial material and shell of encapsulating material, wherein the shell of encapsulating material is impermeable to the antimicrobial material and is optionally physiologically acceptable.
The term “encapsulated” is well known in the art. Encapsulation can be defined as the technology of packaging a substrate (solids, liquids, gases) within another material. In the encapsulate the material which has been entrapped is termed the core material or the internal phase while the encapsulating material is referred to as the coating, the shell material or the carrier. Such encapsulated materials are also commonly referred to as core/shell materials.
In one aspect the present invention provides a process for producing of an antimicrobial material in an encapsulated form, comprising co-processing an antimicrobial material with an encapsulating material, to cause said material to encapsulate said antimicrobial material within a shell, and recovering the antimicrobial material, wherein the shell of encapsulating material is impermeable to the antimicrobial material and is optionally physiologically acceptable.
In one aspect the present invention provides a process for introducing an antimicrobial material into a foodstuff comprising (i) providing the antimicrobial material in an encapsulated form comprising a core of antimicrobial material and shell of encapsulating material, (ii) introducing encapsulated antimicrobial material into or onto the foodstuff, preferably by (a) injecting the encapsulated antimicrobial material into the foodstuff or (b) tumbling the encapsulated antimicrobial material with the foodstuff.
In one aspect the present invention provides a foodstuff prepared by a process for introducing an antimicrobial material into a foodstuff comprising (i) providing the antimicrobial material in an encapsulated form comprising a core of antimicrobial material and shell of encapsulating material, (ii) introducing encapsulated antimicrobial material into or onto the foodstuff, preferably by (a) injecting the encapsulated antimicrobial material into the foodstuff or (b) tumbling the encapsulated antimicrobial material with the foodstuff.
In one aspect the present invention provides a foodstuff obtainable by a process for introducing an antimicrobial material into a foodstuff comprising (i) providing the antimicrobial material in an encapsulated form comprising a core of antimicrobial material and shell of encapsulating material, (ii) introducing encapsulated antimicrobial material into or onto the foodstuff, preferably by (a) injecting the encapsulated antimicrobial material into the foodstuff or (b) tumbling the encapsulated antimicrobial material with the foodstuff.